TY - JOUR

T1 - Shallow recycling of lower continental crust

T2 - The Mahoney Seamount at the Southwest Indian Ridge

AU - Woelki, Dominic

AU - Salters, Vincent

AU - Beier, Christoph

AU - Dick, Henry

AU - Koepke, Juergen

AU - Romer, Rene

N1 - Funding Information: We thank Afi Sachi Kocher, Alexandra Zeh, and Julia Wenske for help during sample preparation and measurement. We thank Andreas Stracke and Felix Genske for useful discussions. We would also thank captain Lutz Mallon, the crew and scientists of RV Sonne for their help and support during SO273 cruise Marion Rise and the ordeal of a COVID-related return back to Germany. The cruise was financed by Bundesministerium für Bildung und Forschung ( 03G0273E , 03G0273D ). We acknowledge funding from NSF grant OCE-1657826 (to V.J.M.S.). Part of this work was performed at the National High Magnetic Field Laboratory, which is supported by NSF Cooperative Agreement no. DMR-1157490 and DMR-1644779 and the state of Florida.

PY - 2023/1/15

Y1 - 2023/1/15

N2 - The Mahoney Seamount is a recently discovered volcanic edifice located 4 km north of the ultra-slow spreading Southwest Indian Ridge (SWIR). The SWIR is one of the slowest spreading ridges worldwide with a full spreading rate of ∼14 mm/year and low magmatic productivity. We report that highly vesicular basalts from the Mahoney Seamount have unradiogenic Nd-Hf together with radiogenic Sr isotopic compositions. Their distinct low 206Pb/204Pb isotope signature combined with high 207Pb/204Pb and 208Pb/204Pb is best explained by melting of a mantle that has been strongly influenced by stranded lower continental crust. The geographic distribution of the isotopic variability favors the idea of shallow recycling of lower continental crust isolated for a longer period contributing to melts forming Mahoney Seamount through off-axis fault systems. The isotopic composition of Mahoney Seamount lavas shares many characteristics with EM-1 sources and the DUPAL signature. Previous isotopic studies of the SWIR basalts proposed recycling of ancient subcontinental lithospheric mantle (SCLM) or pelagic sediments with oceanic crust to be responsible for this enriched isotopic signature. Lu/Hf and Sm/Nd ratios of pelagic sediments would result in decoupled 143Nd/144Nd and 176Hf/177Hf ratios. This decoupling is also observed in Ejeda-Bekily dikes from Madagascar, but those are believed to sample the SCLM dispersed in the Indian Ocean. However, Mahoney Seamount shows no decoupling in those isotopic systems and the restricted occurrence of the extreme lower continental crustal signature at Mahoney Seamount implies that the enriched isotopic signature has a different origin.

AB - The Mahoney Seamount is a recently discovered volcanic edifice located 4 km north of the ultra-slow spreading Southwest Indian Ridge (SWIR). The SWIR is one of the slowest spreading ridges worldwide with a full spreading rate of ∼14 mm/year and low magmatic productivity. We report that highly vesicular basalts from the Mahoney Seamount have unradiogenic Nd-Hf together with radiogenic Sr isotopic compositions. Their distinct low 206Pb/204Pb isotope signature combined with high 207Pb/204Pb and 208Pb/204Pb is best explained by melting of a mantle that has been strongly influenced by stranded lower continental crust. The geographic distribution of the isotopic variability favors the idea of shallow recycling of lower continental crust isolated for a longer period contributing to melts forming Mahoney Seamount through off-axis fault systems. The isotopic composition of Mahoney Seamount lavas shares many characteristics with EM-1 sources and the DUPAL signature. Previous isotopic studies of the SWIR basalts proposed recycling of ancient subcontinental lithospheric mantle (SCLM) or pelagic sediments with oceanic crust to be responsible for this enriched isotopic signature. Lu/Hf and Sm/Nd ratios of pelagic sediments would result in decoupled 143Nd/144Nd and 176Hf/177Hf ratios. This decoupling is also observed in Ejeda-Bekily dikes from Madagascar, but those are believed to sample the SCLM dispersed in the Indian Ocean. However, Mahoney Seamount shows no decoupling in those isotopic systems and the restricted occurrence of the extreme lower continental crustal signature at Mahoney Seamount implies that the enriched isotopic signature has a different origin.

KW - basalt

KW - lower continental crust

KW - MORB

KW - off-axis

KW - radiogenic isotopes

KW - Southwest Indian Ridge

UR - http://www.scopus.com/inward/record.url?scp=85145233898&partnerID=8YFLogxK

U2 - 10.1016/j.epsl.2022.117968

DO - 10.1016/j.epsl.2022.117968

M3 - Article

AN - SCOPUS:85145233898

VL - 602

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

SN - 0012-821X

M1 - 117968

ER -